The two main systemic medications for glaucoma are diuretics: Neptazane and Diamox.
Glaucoma is essentially a build up of fluid in the eye, either the aqueous doesn't flow through the drains properly or the eye produces too much aqueous. I'm assuming your relative has open angle glaucoma in which case any of the diuretic herbs may be beneficial. Although his/her best bet would probably be Vitamin C in megadoses (amounts exceeding 1,000mg). Vitamin C is a potent diuretic in high concentrations.
Despite popular belief, herbal eye drops can be highly toxic and do more damage than good. Your relative's only other options are surgery to permanently create a new drain, or marijuana (I say this in all seriousness, it is the only herb that has been proven to actually lower intraocular eye pressure.)
There are other options for traditional pharmaceutical treatment. If the only issue is an allergy to the eye drops, there are several new formulas on the market made specifically for patients who are allergic to the preservative (benzalkonium chloride). There are also antihistamine drops that can be instilled prior to the glaucoma medication that can prevent the allergic reaction.
Hope this helps.